The invention relates to a method for limiting the closing force of movable parts, in particular windows and sliding roofs in motor vehicles, according to the preamble to the independent claim.
Many of the previously known methods are essentially based on the fact that a particular measurement quantity that typically changes in the event of a pinch is monitored and when a particular, preset limit value is exceeded, steps are taken to limit the closing force. These typical values are, for example, the speed of a motor driving the movable parts or the current- or power consumption of this motor. Frequently, the limit values for triggering the closing force limitation are also variable and can be adapted, for example, to changing friction conditions or aging processes.
All of these methods, however, have the disadvantage that the limit values are predetermined in a fixed manner independent of the type of objects being pinched. It is therefore impossible to adapt the closing force limitation to objects of a different hardness or softness.
Consequently consideration is also not given to the fact that the dynamics and therefore also the respective pinching forces can be subject to very intense fluctuations depending on the type of object being pinched.
With the method according to the application, the force increases when hard objects are pinched are replicated by springs with relatively high spring ratios of 65 N/mm, for example, and the force increases when soft objects are pinched are replicated by springs with relatively low spring ratios of 10 N/mm, for example. A permissible pinching force of 100 N is already achieved after a very short travel distance when there is a high spring ratio and only after a relatively long travel distance when there is a low spring ratio.
This results in the fact that with a fixed preset value of a speed change as a limit value, when a very hard object is pinched, the drive for adjusting the movable parts must be switched off very rapidly in order not to exceed the preset pinching force. On the other hand, when very soft objects are being pinched, it can take a very long time before a pinch prevention measure is activated.
Thus the current methods do not take different spring ratios into consideration. Depending on the spring ratio, the forces acting on the object being pinched can vary within an extremely wide range. This is a big disadvantage because an optimal limit value can only be matched to one particular spring ratio as a switch-off criterion.
The method according to the invention for limiting the closing force of movable parts, with the features of the main claim, has the advantage that by presetting a time limit value curve, an optimal adaptation to different spring ratios is possible. The limit value curve can be selected so that when hard objects are pinched with a high spring ratio, there is sufficient time to activate a pinch prevention measure. When objects are pinched with a low spring ratio, the drive can be switched off at much lower pinching forces. By presetting a particular limit value curve, an individual limit value can thus be predetermined for each spring ratio.
It is particularly advantageous that the method according to the invention is a two-stage method. In the first stage, the respective current motor speeds n are determined based on periodic signals of a sensor connected to the adjusting drive and based on them, a value xcex94n that is typical for the current change in the motor speed is calculated, summated, and stored in a memory. Naturally there is no strict periodicity for the signals, particularly not if there is a loss in motor speed.
If the summated value xcexa3xcex94n exceeds a threshold value S, then the method transitions into the second stage in which the time meter and the limit value curve transmitter are started. The time meter does not necessarily have to be started, it can also run continuously. The only decisive thing is that the time meter is sent a signal indicating the time at which the second stage is triggered or the limit value curve transmitter is started.
In this second stage, of the system is disposed in a kind of alarm state and the movement process is observed in a differentiated manner according to the other process steps in order to specifically detect pinching situations particularly with regard to the type of objects being pinched. To that end, the current limit values g(t) of the limit value curve transmitter are compared to the values of the current, summated values xcexa3xcex94n. It is particularly advantageous that by presetting or starting the time limit value curve g(t), an individual limit value can be preset for each spring ratio because the chronological development of the value xcexa3xcex94n also has a different chronological progression depending on the spring ratio.
The triggering of a measure for limiting the closing force only occurs if the respective current value of the summated value xcexa3xcex94n is equal to or greater than the respective current limit value gj (t) . Then, for example, the drive is switched off or reversed. At the same time, the time meter and the sum memory are reset.
If the respective current values of the summated values xcexa3xcex94n do not reach the respectively current limit values gj(t) and if the values of the summated values xcexa3xcex94n do not change within a predetermined tolerance xcex94 and a predetermined time xcex94t, then the comparison is stopped and the time meter and the sum memory are reset. Then it is assumed, namely, that there was no serious expectation of pinching but only a partial sluggishness in the system.
With each resetting of the sum memory and the time meter, the system reverts to the first stage in which there is merely a monitoring of whether the summated value xcexa3xcex94n exceeds a particular threshold value. In order to prevent this excess from occurring automatically after a certain amount of time as a result of the summation, the sum memory must be continuously decremented in this first stage. Naturally, this decrementation has to occur slowly.
Advantageous improvements of the method according to the main claim are possible by means of the measures disclosed in the dependent claims.
It is advantageous if the determination of the respective current motor speeds n is executed based on periodic edge alternations. Such edge alternations are typically produced by a two-pole or multi-pole annular magnet which is mounted on a rotatable axle of the motor. Upon rotation of the axle, signal changes are produced which are detected by a Hall sensor. The respective current motor speed can be determined from the periodic edge alternations, for example by measuring the period duration.
In practice, it has turned out to be particularly advantageous if, for the change in the motor speed xcex94n, the difference between a current speed value ni and an immediately preceding speed value nixe2x88x921 is calculated. Calculating this difference yields, in a first approximation, the derivative of the motor speed n over the distance traveled by the movable part to be adjusted.
The method according to the invention makes it possible to preset an arbitrary time limit value curve with which a very particular limit value is to be associated with each arbitrary spring ratio. It has turned out to be extremely advantageous if the curve of the limit value g(t) is interpolated from presettable, empirically determined corner points gi. On the one hand, this simplifies the application of the method and on the other hand, a certain flexibility is assured because based on these corner points gi, different functions adapted to the respective system can be plotted through these corner points. Advantageously, the corner points gi are stored as a table in the limit value curve transmitter.
An additional, very significant advantage is achieved if the limit value curve automatically adapts to changing operating conditions. For example, sluggishness due to aging effects can then be recognized and taken into account.
A current and advantageous measure for limiting the closing force of the adjusting drive is to stop or reverse the adjusting drive or also to move the movable part back into an initial position.